New research from the Insurance Institute for Highway Safety (IIHS) suggests that broader cellphone laws — like bans on holding the phone while behind the wheel — can help reduce crash rates.

IIHS researchers examined crash rates in three states — Oregon, Washington, and California — that adopted broad laws as opposed to laws that enumerate a series of specific forbidden operations like texting or talking on the phone.

Specifically, the researchers examined the laws’ effect on police-reported rear-end crashes. Rear-end crashes were chosen because past research has shown that cellphone use is associated with a much larger increase in the odds of those crashes than any other type.

The findings show that monthly crash rates per 100,000 people dropped substantially in Oregon and Washington after those states adopted laws against holding a phone while driving. However, California failed to achieve the same gains.

It appears that broader cellphone laws work, but the specific wording of the law as well the severity of penalties can make a difference.

In 2017, Oregon and Washington banned any “holding” of a cellphone and specified that the bans apply to times when the vehicle is stopped temporarily because of traffic or other momentary delays.

That same year, California’s law used similar general language. However, it did not state whether its ban applies to times when the vehicle is stopped temporarily. Also, by prohibiting “holding and using” a cellphone, rather than simply “holding” one, it made it possible, at least theoretically, for a cited driver to argue that they were holding their phone but not using it, and therefore weren’t violating the law.

To determine how effective the three states new broader laws were, IIHS researchers compared monthly crash rates over 2015-19 with two control states, Colorado and Idaho. Both already had texting bans in place but did not change their laws to prohibit other cellphone use.

The findings were mixed. The rate of police-reported rear-end crashes of all severities did not change in California with the broadening of its cellphone law. However, crash rates dropped 8% in Washington following its legal changes, compared with Colorado and Idaho.

The monthly rates of rear-end crashes with injuries also remained flat in California over 2015-19.

But in Oregon and Washington, a general declining trend accelerated following their adoption of broader “holding” laws. Compared with Colorado and Idaho, monthly rear-end injury crash rates dropped 9% in Oregon and 11% in Washington. California showed an increase of 2%, but that figure was not statistically significant, note researchers.

The bottom line: The greater clarity of the Oregon and Washington laws, especially with regard to temporary stops, may partly explain their greater success in curbing crashes. In addition, penalties for violating the laws in Oregon and Washington are far more severe than in California, which could play an additional role in the laws’ flagging success in the Golden State.